Reactor measurements are central to heterogeneous catalysis research. Apart from reactors which feature a number of discrete sampling points, typically less than ten, all reactor designs have in common that reaction products are analyzed in the reactor effluent stream be it gaseous or liquid. The reaction pathway, i.e. how the reactants are transformed into products remains hidden and only a single kinetic data point is obtained for a set of reaction variables. In addition to kinetic information, heterogeneous catalysts are often characterized spectroscopically to investigate their geometric and electronic structure, surface species and active sites. As a catalyst is a dynamic system and adapts to its chemical environment, in situ spectroscopic techniques become more and more important in heterogeneous catalysis research. These techniques aim at bridging the material and pressure gap by studying polycrystalline powders or supported catalysts under working reaction conditions.
U.S. Pat. No. 4,676,955 discloses an instrument to measure catalytic reaction rates. The reactor is built on the recycle reactor principle and has an internal recycle blower that is floating on a feed fluid. The recycle blower creates a large internal recycle flow and thereby eliminates all internal temperature and concentration fluctuations. During operation of the reaction vessel the catalyst is inserted into a catalytic basket situated inside the reaction vessel. After placing the catalytic basket inside the reaction vessel, the vessel is closed and then flushed with an inert gas, such as nitrogen, to remove all air and undesirable reactive gases contained therein. A feed gas is then fed into the reaction vessel until a desirable pressure is obtained. Further, the reaction vessel is heated until a temperature reaches a desirable range for the specific reaction to be analyzed. Once a desirable pressure and temperature has been reached, the reaction is allowed to continue for a suitable amount of time. During the reaction period, the fluid in the upper portion of the vessel cavity is drawn downwardly through the catalyst bed by impeller vanes and then outwardly to the side of the bottom portion of the cavity. The fluid is then forced upwardly and once again is drawn downwardly into the catalyst bed. Such recycling continues throughout the reaction with a small amount of product being removed through an outlet port for analysis. The mean cover of the reaction vessel is equipped with a desirable number of ports to accommodate various desired functions. Thus, a thermocouple may extend into the catalytic bed portion of the reaction vessel to measure the temperature therein.
M. Bosco, F. Vogel, Catalysis Today, 116 (2006) 348-353, describe an optically accessible channel reactor for the kinetic investigation of hydrocarbon reforming reactions. The reactor allows surface temperature measurements along the reactor through a quartz window using IR thermography. The catalyst is coated as a thin layer onto a metal plate placed at the bottom of the reactor channel. The massive metal body of the channel reactor may be heated by heating cartridges such that a uniform temperature distribution along the channel can be maintained. A small stream of gas can be withdrawn with a moveable capillary to measure the concentration profile in the reactor. The catalyst surface temperature is measured using an infrared camera. By using a quartz glass window the spectral range of the camera has to be in the near infrared region. To take into account the emissivity of the catalyst surface a calibration is performed. A thermocouple is placed in close contact to the catalyst surface and the reactor is heated to different temperatures until the reactor is well thermally equilibrated. A power law is fitted to the data points. After an infrared picture of the catalyst surface is taken, the measured intensities are read out along the center line of the reactor flow direction. The temperature difference is calculated between the measured temperature of the catalyst surface during the reaction and during flushing the reactor with pure argon at a constant setting of the heating system. The disadvantage of the described reactor lies in the fact that radiation heat losses are induced by measuring the temperature from outside through a window affecting indirectly flow and surface chemistry compared to an insulated reactor.
R. Horn, K. A. Williams, N. J. Degenstein, L. D. Schmidt, Journal of Catalysis 242 (2006) 92-102 investigated the mechanism of catalytic partial oxidation of CH4 on Rh-coated α-Al2O3 foam monoliths by measuring species and temperature profiles along the catalyst axis and comparing them with numerical simulations. A thin quartz capillary connected to a quadrupole mass spectrometer is moved through the catalyst with a spatial is resolution of about 0.3 mm. The reaction is carried out in a quartz tube. High-purity reactants CH4, O2 and the internal standard Ar are fed through calibrated mass flow controllers through a side port at the bottom of the tube and leave the reactor from the top for incineration. An injection needle inserted through a septum at an end port at the bottom of the tube enables guided movement of the capillary without noticeable gas losses. α-Al2O3 foams loaded with Rh are used as catalysts. To avoid axial radiative heat losses in the reaction tube, two uncoated α-Al2O3 foams are used as heat shields. To avoid bypassing of gas, the catalyst and the heat shields are tightly wrapped in alumo-silicate paper. The reaction profiles are measured by sliding a 20 cm long fine quartz capillary through a channel, diamond drilled through the centerline of the catalyst. The lower end of the capillary is connected to a ported micro volume tee. The opposite port is used to feed a thermocouple into the capillary. The tip of the thermocouple is aligned flush with the open end of the capillary to measure species composition and temperature simultaneously at each point in the catalyst. The side port of the tee is connected to a stainless steel capillary, which is inserted into the inlet valve of a mass spectrometer vacuum chamber. At the end of the stainless steel capillary, a rotary vane pump generates a vacuum of about 500 mTorr, forcing a permanent flow from the end of the quartz capillary positioned in the catalyst to the sapphire seat of the MS inlet valve. The tee is mounted on a micrometer screw so that the capillary can be moved up and down with sub-millimeter resolution. All profiles are measured by sliding the capillary tip down (i.e., against the flow direction) from a position 3 mm downstream to the end of the catalyst through the catalyst up to about 5 mm into the front heat shield. Using this technique, the open channel is left downstream of the capillary tip and does not influence the sample composition at the tip position.
In a further paper, Journal of Catalysis, 249 (2007) 380-393, R. Horn, K. A. Williams, N. J. Degenstein, A. Bitsch-Larsen, D. Dalle Nogare, S. A. Tupy and L. D. Schmidt describe a modified reactor and capillary sampling system. The sampling capillary comprises a side sampling orifice and a thermocouple aligned with the sampling orifice. The quartz sampling capillary and thermocouple meet in a stainless steel tee, the third port of which is connected to a stainless steel capillary that discharges into the inlet valve of a mass spectrometer. A pump generates a vacuum at the end of the stainless steel capillary, forcing the gases from the sampling orifice into the mass spectrometer. Moving the capillary/thermocouple assembly up and down allows measuring species and temperature profiles along the centerline of the catalyst. The measured temperature is a gas temperature as the thermocouple is in thermal contact with the flowing gas but not with the catalyst surface. The reaction cell is self-supported on a steel mounting frame with stainless steel inlet and outlet tubes. The sampling capillary is guided in steel capillary liners to avoid any bending leading to uncertainties in the sampling orifice position. The compact and rigid self-supported construction of the reactor provides precise geometric alignment and is easy to dismantle and reassemble. The capillary is moved by a stepper motor mounted underneath the reactor. This allows automatization of the experiment such that larger experimental campaigns may be conducted.
To understand heterogeneous catalysis in more detail it is desirable to follow in situ how the reactants are transformed into products and how the catalyst changes along the reaction coordinate. Although it has been demonstrated that spatially resolved measurements of gas species and temperature may be performed in situ inside a reactor, the catalyst has been treated so far as a black box.
The problem underlying the invention therefore is to provide a reactor design that enables in situ monitoring of a sample, e.g. a catalyst, in a reactor under working conditions. The reactor design should also monitor changes of the fluid species (gas or liquid) and solid and fluid temperature measurements.